This invention relates generally to automotive air conditioning systems and more particularly to electrical switches responsive to fluid pressure of air conditioning refrigerant and to sensors for monitoring the temperature of the fluid.
Automotive air conditioning systems include a refrigerant fluid pressure sensor to ensure that there is a minimum system pressure to permit the system to function properly and a temperature sensor used for cycling the compressor. With regard to the pressure sensor, it is conventional to use an electrical switch comprising a pressure responsive snap-acting disc member mounted in a housing with one face of the disc in fluid receiving communication with refrigerant fluid being monitored. The disc, upon snapping from one dished configuration to an opposite dished configuration, opens or closes an electric circuit path to provide an on/off control for the system. An example of one such pressure sensor is shown in U.S. Pat. No. 6,313,419, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by this reference.
With regard to the temperature sensor, a temperature sensing probe is conventionally wedged between heat exchanger fins of the evaporator of the air conditioner in close thermal coupling therewith to provide a temperature input of the refrigerant. Although sensing the temperature of the refrigerant through the heat exchanger works well enough to provide satisfactory comfort conditions, there are several limitations to this approach. One such limitation is the fact that the temperature readings of the sensor varies when the sensing portion of the probe, i.e., the thermistor, is dry or wet, as by condensation. Another limitation is the temperature gradient between the sensor and the refrigerant causing a thermal lag in sensing changes in temperature of the refrigerant fluid. Yet another limitation relates to movement of the sensor over time caused by vibrations and the like.
An object of the present invention is the provision of a combined fluid pressure responsive switch and temperature sensor. Another object is the provision of a device which not only senses the pressure of the refrigerant but also senses the temperature of the fluid. Yet another object of the invention is the provision of a switch and sensor which is free of the prior art limitations noted above.
Briefly stated, a combined pressure responsive electrical switch and temperature sensor made in accordance with a preferred embodiment of the invention comprises a base member having a recess in which an electrical switch is mounted with a pressure responsive snap-acting disc disposed over the recess, the side of the disc facing away from the recess being exposed to a fluid pressure source in a pressure chamber formed between the base and a port fitting. The disc is adapted to snap from an outwardly convex configuration to an outwardly concave configuration at a selected fluid pressure with the disc moving into electrical engagement with movable contacts of the electrical switch to close a circuit path therebetween. The port fitting has a closed ended bore having a threaded sidewall extending along a longitudinal axis with a passageway formed between the closed end of the bore and the pressure chamber. An elongated temperature sensing portion of the port fitting extends into the threaded bore along the longitudinal axis and is spaced from the side wall and a temperature responsive member such as a thermistor is disposed in the temperature sensing portion. The size of the temperature sensing portion is selected so that it fits within the bore of a fluid pressure source nipple which is received in the threaded bore while still allowing fluid flow between the sidewall of the nipple bore and the temperature sensing portion. In one preferred embodiment, the temperature sensing portion is hollow so that the thermistor is open to the fluid source while in another preferred embodiment the temperature sensing portion is hollow with a closed end with the thermistor disposed adjacent the closed end in close thermal coupling therewith. In yet another embodiment, the temperature sensing portion is generally solid. Leads extend from the thermistor up into the pressure chamber beyond a gasket which defines the outer perimeter of the pressure chamber for engagement with extensions of terminals mounted in the base member. In other preferred embodiments, the thermistor is molded in a plastic finger extending from a housing member and arranged to extend into a fluid source.
The port fitting is received on a threaded nipple with the temperature sensing portion extending into the nipple while allowing fluid to pass therebetween and into the pressure chamber for monitoring fluid pressure as well as sensing temperature of the fluid.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings wherein like reference numerals refer to like parts.